This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 99-3957 filed in Korea on Feb. 5, 1999; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of growing a high quality gallium nitride (GaN) film at a high growth rate, which is useful in applications such as homoepitaxy blue laser diodes or electronic devices.
2. Description of the Related Art
Growth methods used to deposit GaN films on a sapphire substrate can be classified into metal organic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE). (references: [1] H. P. Maruska and J. J. Tietjin, Appl. Phys. Lett. 15 (1969), pp. 327; [2] H. M. Manasevit, F. M. Erdmann and W. I. Simpson, J. Electrochem. Soc. 118 (1971), pp. 1864; [3] S. Yoshida, S. Misawa and S. Gonda, Appl. Phys. Lett. 42 (1983), pp. 427). Among these three techniques, HVPE has an advantage of a high growth rate, which is several tens of times higher than that of the other two techniques, so that it is suitable for growing a thick film or bulk monocrystalline. However, HVPE cannot provide high quality GaN films with a mirror surface at the high growth rate.
High quality GaN films having a mirror surface have been obtained by MOVPE and by incorporating a buffer layer into the structure. However, MOPVE is not appropriate for growing a thick GaN film due to its low growth rate in the order of 1 xcexcm/hour. Due to this reason, HVPE has been adapted in GaN film growth on a sapphire substrate in spite of the resulting GaN film having a rough surface and poor crystalline characteristics. Also, to avoid this problem, aluminum nitride (AlN), zinc oxide (ZnO) or low-temperature GaN films have been used as an interface buffer layer, without a distinct quality improvement in the resulting GaN films. (references: [4] H. Amano, N. Sawaki, and Y. Toyada, Appl. Phys. Lett. 48 (1986), pp. 353; [5] S. Nakamura, Jpn. J. Appl. Phys. 30 (1991), pp. 1705; and [6] T. Detchprohm, H. Amano, K. Hiramatsu and I. Akasaki, J. Cryst. Growth 128 (1993), pp. 384).
Conventional procedures for growing GaN films by HVPE are illustrated in FIG. 1. Referring to FIG. 1, first a sapphire substrate is loaded into a reactor for HVPE (S1). Then ammonia (NH3) reaction gas is supplied onto the substrate for nitridating the surface of the sapphire substrate (S2) and then growing a GaN film on the substrate (S3). In either case, in the step S1, prior to the introduction of the sapphire substrate into the reactor, a buffer layer is grown with AlN or ZnO to a thickness of several hundreds of angstroms by sputtering or chemical vapor deposition (CVD). Then, the steps S2 and S3 are carried out. However, the growth of the GaN layer by the HVPE illustrated in FIG. 1 is not enough, resulting in rough surface characteristics as can be seen in FIG. 2A. Furthermore, an X-ray rocking curve shown in FIG. 2B exhibits poor crystalline characteristics at a full width of half maximum (FWHM) value of 1000 arcsec or more (the GaN film 2 xcexcm thick) The term xe2x80x9cnitridationxe2x80x9d refers to the unintentional formation of thin film, for example, an AlN film, on a sapphire substrate by flow of NH3 reaction gas onto the substrate, but not to intentional formation of a buffer layer of AlN.
It is an object of the present invention to provide a method of growing a high quality gallium nitride (GaN) film at a high growth rate, which is able to provide a mirror-like surface by using a modified hydride vapor phase epitaxy (HVPE) technique on the resulting GaN film, wherein good crystalline characteristics can be obtained even at a high growth rate.
In one embodiment, the present invention provides a method of growing a GaN film on a sapphire substrate by HVPE, the method including: loading the sapphire substrate into a reactor; nitridating the resulting sapphire substrate; treating the sapphire substrate by flowing a gas mixture of ammonia (NH3) and hydrochloric acid (HCl) onto the sapphire substrate; nitridating the sapphire substrate treated with the gas mixture; and growing the GaN film on the sapphire substrate.
Preferably, a silicon (SiC) carbide substrate, an oxide substrate or a carbide substrate is used in place of the sapphire substrate.